Dialkyl formamides as selective solvents for refining mineral oils



Patented July 18, 19 39 I v I i UNIITED'STATES PATENT OFFICE I v a saiioI DIALKYL FORMAMIDES as SELECTIVE SOL- VENTS FOR REFINING MINERAL omsVirgil L. Hanslcy, Niagara Falls, N. Y., assignor to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application April 20, 1937,

Serial No. 137,928

15 Claims. (Cl. 196-43) This invention relates to the separation of mix-"dialiphatic as employed herein and in the claims tures of hydrocarbonsby selective solvent extracwill be restricted to hydrocarbon radicalsand tion and more particularly to thesolvent refining will includeunsaturated and cyclic aliphatic hyof mineral oils. drocarbon radicalsas well as the saturated and 5 It is now well known that a largeproportion "open chain aliphatic hydrocarbon radicals. 5 of the mineraloils and gasolines of today are com- The hydrocarbon mixture or oil ismixed with plex mixtures. of parafllnic and non-parafllnic the formamideunder such conditions that two I hydrocarbons. It is frequentlydesirable to sepalayers are formed; one of which comprises the rate thenon-parafllnic hydrocarbons from the constituents which it is desired toextract from paraflinic hydrocarbons for various reasons. One the oildissolved in the bulk of the liquid solvent, 10 o! the main reasons isthat the paraflinid hydrowhile the other comprises the undissolved andcarbons are in general more resistant to decomrelatively paraflinic oilin admixture with a relaposition through heat and oxidation than thetively small amount of the solvent. Preferably, non-paraflinichydrocarbons. Accordingly, the my method comprises mixing thesubstituted oil containing the larger proportion of parafiinic formamidewith the hydrocarbon mixture inap- 15 constituents or, in other words,the relatively proximately equal volumes and heating with agimoreparafllnic oils are more stable than the less tation to a temperature atwhich the solvent and paraflinic oils and hence are more desirable asoil become substantially completely miscible. lubricants and for otherpurposes This solution is then cooled with agitation to a Variousmethods have been proposed for sepatemperature at least C. below thetemperature 20 rating the non-parailinic from the parafllnic conofcomplete miscibility. The resulting mixture is stituents of oils. One ofthe more common and allowed to stand until it separates 'into twolayers. oldest is by treatment with sulfuric acid which The two layersare separated by separately withremoves some of the non-parailiniccompounds drawing each layer. The dialiphatic iormamide from the oils.More recently it has been proposed is recovered from each layer,preferably by disto separate the non-parafllnic hydrocarbons bytillation. The residue from the layer containing means of selectivesolvent extraction. the larger amount of solventconsists of a large AnObject of the Present invention is to Provide proportion 01'non-parafllnic and undesirable conmethod Sep a mixture of Da aflstituents. The residue from the layer containing 8nd -pa fin cydrocarbons into portions, the smaller amount of solvent consistsprimarily one of which is relatively more -paraiiinic than of thedesirable paraflinic hydrocarbons. the original mixture and the otherrelatively less In the examples given below, the selective p AnotherObject is the Separation 0f moval oi non-paramnic constituents from aminrelatively nonparaflinic bodies from mineral lul 11 has been measuredby following the brlcating oilsto produce lubricating oils of relachangei viscosity-gravity constant of the oil. 85 tively high parafliniccharacter. Afurther object This t t h s b d ib d by J 3, Hill istheproduction of lubricating oils with improved and Coates in I d t i lnd En i i viscosity-temperature curves from oils with poor Chemistry, Vl me 20, page 641, et seq., in an viscosity-temperature curves. Stillother objects article e t t Viscosity-Gravity Constant 0 will pphereinafterof Petroleum Lubricating Qils. If a given crude 40 TheseObjects y be accomplished in accord petroleum be distilled intosuccessive fractions ance with my invention which comprises P and thespecific gravities and viscosities of the ing mixtures'of parafiinic andnon-parafiinic hyseveral fractions determined, it will be found thatdrocarbons with an N-dialiphatic substituted they nf to the'generalrelationship: formamide boiling below about 250 C. to remove 752 I thenon-parafilnic hydrocarbons by the selective i 10g (v 38) action of theformamide. The dialiphatic formamides of my invention may be representedby in which G is the specific gravity at F.,

the formula V" is Saybolt Universal viscosity at F., and

o R a is the viscosity-gravity constant. These con- 5 H K stants arelower for fractions of parafllnic crudes than are the constantsiorfractions of the naphthenic crudes. The viscosity-gravity constantis, whereinR and R represent aliphatic hydrocarbon therefore, an indexof the paraflinicity oi an oil, radicals. It will be understood that theterm and a decrease in the value of this constant for a 55 givenfraction of lubricating oil indicates an increase in parafiinhydrocarbon content.

Example 1 temperature solvent and oil were miscible. The

solution was cooled to 80 C., allowed to settle one-half hour, and thetwo layers withdrawn into separate containers. Dimethyl formamide wasremoved from both layers under reduced pressure. The top layer was foundto contain 80% of the volume of the original oil and to have aviscosity-gravity constant of 0.848.

Example 2 V The lubricating oil distillate given in Example 1 was heatedwith agitation with twice its volume of dimethyl formamide to 100 (3.,cooled to Example 3 The distillate used in Example 1 was heated with anequal volume of diethyl formamide to 100 C. with agitation, cooled to 70C. and allowed to settle one-half hour. After separation of the twolayers and removal of solvent from each, an oil recovery of 76% wasobtained from the top layer, this oil having a viscosity-gravityconstant of 0.858.

- Dialiphati c formamides may be used with advantage in conjunction.with other solvents which areknown to possess selective solvent actionin petroleum refining but which frequently have disadvantages'of lowseparation temperatures and relatively poor yields of refined oil. Someof such other solvents are beta-beta'-dichloro-diethyl ether,nitrobenzene, cyclohexanol, methyl acetate, phenol, cresylic acids,cyclohexanone and aniline. Generally, the dialiphatic formamide shouldconstitute from about or more of such solvent mixture and preferablyabout 50% thereof. Used in conjunction with such solvents, dimethylformamide materially raises the separation temperatures, avoiding thenecessity of refrigeration, and improves the yield of refined oils. Thefollowing examples will illustrate these points:

Example 4 A solvent was prepared by mixing one part of dimethylformamide with one part of nitrobenzene. The lubricating oil distillategiven in Example 1 was heated with an equal volume of this mixed solventto 45 0., the temperature of complete miscibility. The solution wascooled to 20 C., settled one-half hour, and the separated layers treatedas in the previous examples. From the top layer a yield of 70% ofraflinate was obtained having a viscosity-gravity constant of 0.840.Nitrobenzene on the same stock under similar conditions required aseparation temperature of 0 C. and yielded only 58% of raifinate of thesame viscosity-gravity constant.

Example 5 A solvent was prepared by mixing equalparts Example 6 Equalvolumes of dimethyl formamide and cyclohexanol were mixed for use as asolvent. The lubricating oil distillate described in Example 1 wastreated with an. equal volume of the mixed solvent in the mannerpreviously described, the temperature of complete miscibility being 75C. Separation into two phases was accomplished at C. -The yield ofraflinate from the top layer was 64% with a viscosity-gravity constantof 0.854. In attempting to use cyclohexanol alone on this stock,separation into two phases couldnot be accomplished even by chilling toWhile I have disclosed the use' of dimethyl and diethyl formamides, inthe above examples, other dialiphatic formamldes with boiling points upto 250 C. may be employed in place thereof. Some of such other compoundswhich would be suitable are dipropyl formamide, diisopropyl formamide,dibutyl formamide, di-isobutyl formamide, methyl ethyl formamide, methylpropyl formamide, methyl isobutyl formamide, ethyl isopropyl formamide,ethyl butyl formamide, isopropyl isobutyl formamide, divinyl formamide,diallyl formamide, and similar compounds. However, the dialkylforniamides are preferred and of these dimethyl formamide and diethylformamide are the most satisfactory. Further, the dialiphatic formamidesused for extraction need not be pure compounds but may be mixturesboiling between about 150 C. and

about 250 C.

The conditions of application of the solvent will vary with the natureof the oil. Highly naphthenic oils will, in general, require a lowertemperature to effect separation than highly parafllnic oils. Thetemperatures employed will, in general, range from about 0 C. to about200 C; At the higher temperatures, it may be necessary to employpressure to prevent substantial vaporization of the solvent. The ratioof solvent to oil may be varied within rather wide limits and willdepend largely upon the nature of the oil being treated, the amount ofnon-parafllnic constituents therein and the quality of the refined oildesired. In general, the ratio of solvent to oil will lie between 1 to10 and 5 to 1 parts by volume.

The application of the 'dialiphatic formarnides as selective solvents isnot confined to lubricating oil distillates. They may be employed torefine other hydrocarbon or mineral oil fractions such as crackednaphthas, gasoline, or kerosene fractions, whose boiling ranges aresufiiciently difierent from the solvent to permit separation of thesolvent from the hydrocarbon mixture. Extraction treatment with thedialiphatic formamide may be applied to a raw distillate or to a par-.

it may be desirable to supplement the extraction with the usual acid,alkali, doctor, or clay treatment applied either before or after thesolvent extraction.

From the above disclosure, it will appear that I have provided new andimproved selective solvents ior refining petroleum oils and particularlyfor the production of high grade lubricating oil from mediocre crudes.The dialiphatic formamides possess high miscibility temperatures with0115 thus permitting their utilization as extraction solvents over awide temperature range. Further, the dialiphatic iormamides may beemployed in combination with other selective solvents having lowermiscibility and extraction temperatures to permit extraction at highertemperatures and with improved yields of refined oil.

While I have disclosed the preferred embodiments of my invention and thepreferred modes of carrying the same into effect, it will be readilyapparent to those skilled in the art that many variations andmodifications may be made therein without departing from the spirit ofmy invention. Accordingly, the scope of my invention is to be limitedsolely by the appended claims con strued as broadly as is permissible inview of the prior art.

I claim:

1. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-paraifinic compoundswhich comprises extracting the hydrocarbon mixture with an N-dialiphaticformamide boiling below 250 C. to separate the relatively nonparafiiniccompounds from the relatively paraffinic compounds.

2. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-paraflinic compoundswhich comprises mixing an N-dialiphatic formamide boiling below 250 C.with the hydrocarbon mixture, causing the resulting mixture to separateinto two layers and separating the lay ers, whereby the relativelynon-parailinic compounds are separated from the relatively paraffiniccompounds.

3. The method of treating a normally liquid hydrocarbon mixturecontaining relatively parafiinic and relatively non-parafiinic compoundswhich comprises mixing with the hydrocarbon mixture an N-dialiphaticformamide boiling below 250 C., heating the resulting mixture to atemperature where the formamide becomes completely miscible with thehydrocarbon mixture, cooling the mixture to a temperature at least 20 C.below the temperature of complete miscibility and to where the mixtureseparates into two layers, separating thetwo layers, and removing theformamide from each layer, whereby the relatively non-paraffiniccompounds are separated from the relatively paraflinic compounds.

4. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraffinic and relatively non-paraflinic compoundswhich comprises extracting the hydrocarbon mixture withN-dimethyliormamide to separate the relatively non-paraflinic compoundsfrom the relatively parafiinic compounds.

5. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraifinic and relatively non-paraffinic compoundswhich comprises mixing N-dimethyl formamide with the hydrocarbonmixture, causing the resulting mixture to separate into two layers andseparating the layers, whereby the relatively non-paramnic compounds areseparated from the relatively paraffinic compounds.

6. The method of treating a normally liquid hydrocarbon mixturecontaining relatively par hydrocarbon mixture containing relativelyparaflinic and relatively non-parafiinic compounds which comprisesextracting the hydrocarbon mixture with a solvent mixture comprising andialkyl formamide boiling below 250 C. and a selective solventhaving asubstantially .lower separation temperature, to separate the relativelynon-parafiinic compounds from therelatively parafiinic compounds.

8. The method of treating a normally liquid hydrocarbon mixturecontaining relatively parafiinic and relatively non-parafilnic compoundswhich comprises extracting the hydrocarbon mixture with a solventmixture comprising an N-dialkyl formamide boiling below 250 C. andnitrobenzene, to separate the relatively nonparafiinic compounds fromthe relatively paraflinic compounds.

9. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-paraflinic compoundswhich comprises extracting the hydrocarbon mixture with a solventmixture comprising dimethyl formamide and a selective solvent having asubstantially lower separation temperature, to separate the relativelynon-paraflinic compounds from the relatively parafiinic compounds.

10. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-parafiinic compoundswhich comprises extracting the hydrocarbon mixture with a solventmixture comprising dimethyl formamide and beta-beta-dichlorodiet ylether to separate the relatively non-para lo compounds from therelatively parafflnic compounds.

11. -The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-paraffinic compoundswhich comprises extracting the hydrocarbon mixture with a solventmixture comprising dimethyl formamide and nitrobenzene, to separate therelatively non-parafiinic compounds from the relatively parafliniccompounds.

12. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraffinic and relatively non-paraffinic compoundswhich comprises mixing with the hydrocarbon mixture a solvent mixturecomprising an N- dialkyl formamide boiling below 250 C. and a selectivesolvent having a substantially lower separation temperature, heating theresulting mixture to a temperature where the solvent mixture becomescompletely miscible with the hydrocarbon mixture, cooling the mixture toa 13. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-paraflinic compoundswhich comprises mixingwith the hydrocarbon mixture a solvent mixturecomprising an N- dialkyl formamide boiling below 250 C. andcyclohexanol, heating the resulting mixture to a temperature where thesolvent mixture becomes completely miscible with the hydrocarbonmixture; cooling the mixture to a temperature at least 20 0. below thetemperature of complete miscibility and to where the mixture separatesinto two layers, separating the two layers and removing the solventmixture from each layer, whereby thexelatively non-parafllnic compoundsare separated from the relatively paraflinic compounds.

14. The method of treating a normally liquid hydrocarbon mixturecontaining relatively paraflinic and relatively non-paraflinic compoundswhich comprises mixing with the hydrocarbon the two layers and removingthe solvent mixture from each layer, whereby the relativelynonparafllnic compounds are separated from the relatively parafliniccompounds.

15. The method of refining petroleum oil con-' taining relativelyparafllnic and relatively nonparaflinic compounds which comprisesextracting the oil with an N-dialkyl formamide boiling below 250 C. toremove the relatively non-paraflinic compounds from the oil.

VIRGIL L, HANSLEY.

